Isolation and characterization of the bovine Stearoyl-CoAdesaturase promoter and analysis of polymorphisms in the promoter region in dairy cows

Abstract

Conjugated linoleic acid (CLA) in milk arises through microbial biohydrogenation of dietary polyunsaturated fatty acids (PUFA) in the rumen, and by the action of mammary Stearoyl-CoA desaturase (Scd). A large variation (up to ten-fold) in the concentration of this fatty acid in milk have been observed, even in cows receiving the same diet. The reasons for this variation are not well understood. In this study, the bovine core promoter region was isolated by a genome walking strategy from genomic DNA GenomeWalker libraries and then cloned and characterised. This core promoter sequence extended approximately 600bp upstream of the translation start site. The presence of putative transcription factor binding sites conserved in bovine, human, and mouse promoters were observed. Evidence that this promoter fragment was functional in vivo was obtained from expression studies in a mammary cell line. The promoter sequence of the scd gene was compared between cows selected for the ability to produce high fatty acid methyl esters (FAME) (2.22-2.72) in their milk, with the same promoter region of low FAME producing cows (0.81-1.12). However, such comparisons of the sequences of the scd promoter region of cows producing high milk CLA compared with low CLA revealed no polymorphisms in this promoter segment. Furthermore, no sequence polymorphisms were observed between the scd promoter region of Holstein Friesian, Montbeliarde, Normande, Norwegian Red, Charlois, Limousin and Kerry breeds.